1. Field of the Invention
The present invention relates to a piezoelectric substrate, a piezoelectric element and a liquid discharge head to be used for a liquid discharge apparatus and also to methods of manufacturing the same. More particularly, the present invention relates to a high density piezoelectric element having a large area and a liquid discharge head using such an element.
2. Description of the Related Art
There is an increasing demand for long printing heads to be used in ink jet printers in order to improve the resolution and the printing speed of such printers. For this reason, there is a demand for micronized multi-nozzle head structures. Then, piezoelectric elements for discharging liquid are required to be downsized in order to micronize liquid discharge heads. Then, piezoelectric substrates showing a high piezoelectric constant are required in order not to reduce the drive power if liquid discharge heads are micronized. Thus, there is a demand for highly crystalline piezoelectric films as piezoelectric substrates. Such piezoelectric films are required to show a controlled crystallinity so as to contain highly oriented crystals. For a piezoelectric film to be a highly oriented crystal, it is preferable that the directly underlying layer is highly crystalline and the piezoelectric film and the directly underlying layer make a good combination in terms of lattice matching at the time of manufacturing the piezoelectric film.
Additionally, the piezoelectric film and the directly underlying layer are apt to give rise to a phenomenon of film exfoliation when stress is applied to the interface if the piezoelectric film is made thin. Therefore, the directly underlying layer is required to be highly adhesive relative to the piezoelectric film in order to suppress such film exfoliation.
Conventionally, paste of powdery PbO, ZrO2 and TiO2 is molded to form green sheets, which are then sintered to produce a PZT type piezoelectric material for piezoelectric films to be used for piezoelectric elements as described in Japanese Patent Application Laid-open No. S62-213399.
However, it is difficult to produce PZT type oxide films with a thickness of not greater than 10 μm by means of the method disclosed in Japanese Patent Application Laid-open No. S62-213399. Additionally, since such green sheets are sintered at a temperature level not lower than 1,000° C., there arises a problem that the piezoelectric films shrink to 70% of the original size. Then, it is difficult to align a piezoelectric film and a structure such as an ink chamber with an accuracy level of several microns. Thus, no satisfactory micro piezoelectric elements have been available to date.
Furthermore, the influence of the crystal grain boundaries becomes unnegligible as ceramic piezoelectric films formed by sintering green sheets show a reduced thickness to consequently make it impossible to realize good piezoelectric characteristics. As a result, there arises a problem of being unable to obtain piezoelectric characteristics that are satisfactory for causing a piezoelectric film to operate for discharging recording liquid if the piezoelectric film is prepared by sintering a green sheet to a thickness not greater than 10 μm.
Known methods for preparing piezoelectric films include sputtering methods, CVD methods, MBE methods and sol-gel methods in addition to the above cited method. As a matter of fact, it is possible to produce a thin oxide film with a film thickness of not greater than 10 μm by means of any of such methods. However, since the piezoelectric film prepared by means of any of such methods shows a high density to by turn give rise to very large in-plane stress and make the piezoelectric film poorly adhesive to the underlying layer, which is a lower electrode. For the piezoelectric elements of an ink jet head to withstand the stress produced when they are driven repeatedly, it is necessary that the piezoelectric film is highly adhesive to the underlying layer of a lower electrode. However, a piezoelectric film prepared by any of the above-cited methods cannot be feasibly used as piezoelectric element for ink jet recording.
Additionally, if the piezoelectric characteristics of a piezoelectric material fluctuate due to temperature change, the temperature of the operation environment needs to be held to a constant level, although the temperature requirement may vary depending on the type of piezoelectric material. In other words, a piezoelectric material that is lowly temperature-dependent and shows excellent piezoelectric characteristics when used as piezoelectric element has not been found to date.